Owing to technical improvement in the fields of video/audio data compression, digital modulation/demodulation, and so on, a digital television broadcast system broadcasting TV signals in the form of digital data stream is being standardized rapidly.
In the digital television broadcast system, audio/video (A/V) signals to be broadcasted are compressed according to the data compressing rule specified by MPEG 2 (Moving Picture Experts Group) and the compressed A/V data are broadcasted in the form of transport stream (TS), which is also defined in MPEG 2 standard, composed of successive 188-byte-long transport packets (TPs).
The digital TV broadcast system, which will be commercialized soon owing to technical improvement of A/V data compression and transmission, is able to support much higher-quality of video and audio than an analog TV system. Furthermore, it ensures data compatibility with a digital communication device, a digital storage device, etc.
By the way, a new device is being developed to prepare for commercialization of digital TV broadcast system. That is a digital recorder being able to receive TS of digital broadcast programs and to record it on a writable HD-DVD. Such a digital recorder will be widely used as the digital TV broadcast system is commercialized in earnest.
A single physical broadcast channel (called ‘RF channel’ in general) has about 6 MHz bandwidth which ensures 19.4 Mbps data rate. This data rate can carry a single HD-TV broadcast signal or about four SD-TV signals. Such a logical or virtual channel carrying one SD-TV signal in an RF channel is called sub-channel.
In other words, a single RF channel sometimes includes several digital channels, namely, sub-channels which carry mutually-different broadcast programs. Therefore, a DVD recorder being developed must be able to record/reproduce two or more sub-channels simultaneously at a user's request. In addition, it may be able to record/reproduce two or more sub-channels chosen from different RF channels, respectively.
By the way, an apparatus being able to receive and present digital TV broadcast programs, e.g., a digital TV set can not select a sub-channel and decode a received RF stream until PSI (Program Specific Information) for a digital stream of TV program is received. Moreover, it can keep an exact presentation timing of packets constituting a digital stream after synchronizing an internal clock with PCRs (Program Clock Reference) where respective PCRs carried by the digital stream are received within an allowable interval.
In general, a digital recorder records one channel and reproduces it later. In case that a digital recorder is able to record a plurality of channels, it may reproduce one channel chosen among recorded channels, or reproduce at least two channels simultaneously to present them in a multi-screen, e.g., PIP (Picture-In-Picture) on a digital TV set.
In this multi-channel providing, PSI providing way must be differentiated and PCRs inserted in each channel stream may be compensated depending upon whether all multi channels belong to a single RF channel or not.